A number of NIH funded researchers at the University of California, San Francisco have joined together and rented a Meridian Instruments, Inc. ACAS-470 cytometer in order to test its efficacy in their research and to obtain preliminary information for this SIG proposal. The rental, which ended 31 March 1989, was successful. Excited by the quality and uniqueness of their results, they enlisted the participation of their colleagues who now comprise the Principal Users of this application. The Principal Users constitute a large group of active researchers and include a number of distinguished investigators. An ACAS-570 system will be purchased and made available to the Principal Users. The system will permit acquisition and analysis of fluorescence images of cells as a function of time under various physiological conditions making it possible to follow the time course of time-dependent effects of hormones, activators or other manipulations on intracellular physiological parameters particularly Ca2+ and pH levels. It will enable physical isolation of specific cells, and will permit FRAP (Fluorescence Recovery After Photobleaching) analysis of the diffusivity of membrane components. Further, using photolytic release of caged ions or other mediators such as inositol triphosphate, c-AMP, c- GMP, IP3, etc. which can be incorporated into cells, the ACAS-570 will empower the researchers to manipulate and follow cell physiologic responses to localized release of these biochemical mediators. Using the rare analysis capability of the requested instrument will facilitate location of cells producing proteinaceous infective elements called prions; this research is of great interest in the study of Alzheimer's disease. Another investigator will use the ACAS to follow the fusion of drug-loaded liposomes with infected CD4+ cells as a therapy for AIDS. A total of 14 researchers representing 23 NIH research grants will be served by this instrument.